solar radiation; horizontal and tilted; azimuth angles; celestial sphere
The calculation of solar radiation received at a particular place and at a particular time, involves many factors like rotation and revolution of the earth, atmospheric attenuations, atmospheric conditions, time of day and year, geographic location of place, and site location of collector, tilt of collector, type of its variation due to seasonal and atmospheric conditions and show how calculation for horizontal and tilted surfaces may be done based on geometrical and seasonal consideration. Certain angles have been defined for specification of the sun's position in the sky like solar altitude and azimuth angles and the sun's apparent path across the sky found on the celestial sphere. The method of defining position of a point on the earth's surface with respect to the sun's rays by means of latitude, hour angle and declination is also shown. Depletion of extraterrestrial radiation by absorption, scattering etc. is also discussed in detail in this paper.